It is known to provide an internal combustion engine with a supercharging device which acts to increase the density of air for combustion in cylinders of the engine and thereby improve fuel burning efficiency and engine power.
A known supercharging arrangement 10 is shown in FIG. 1. The supercharging arrangement 10 is associated with one or more cylinders 12, each of which houses a piston 14 movable during use towards and away from a head portion 16 of the cylinder 12. An inlet valve 18 and an outlet valve 20 are included for controlling flow of gases into and out of the cylinder 12, the inlet valve being associated with an inlet conduit 22 and the outlet valve 20 being associated with an outlet conduit 24.
The supercharging arrangement 10 also includes a conventional throttle valve 26 arranged to control flow of air into the cylinder 12 and thereby the power generated by the cylinder 12.
Disposed between the throttle valve 26 and the cylinder 12 in line with the inlet conduit 22 is a supercharging device 28 which may be of any type, such as a screw type supercharger having a pair of intermeshing helical screw members.
During use, the supercharging device 28 controllably increases the flow rate of air into the cylinder 12 and in this way increases the density of air in the cylinder 12 and the power provided by the cylinder 12, with the amount of air available to the supercharging device 28 being controlled by the throttle valve 26.
While this arrangement works well for conventional performance vehicles and for high performance vehicles at elevated rpm, the arrangement generally does not operate well for high performance vehicles at relatively low rpm.
Without wishing to be bound by theory, the inventors of the present invention believe that the reason for poor performance of a supercharging arrangement of the type shown in FIG. 1 for high performance vehicles at relatively low rpm is because high performance vehicles generally have a relatively long inlet valve opening duration which causes both the inlet valve 18 and the outlet valve 20 to be simultaneously open at certain times and the inlet valve 18 to be open at the beginning of a compression stroke. At relatively low engine rpm the pressure of air passing through the inlet conduit 22 in the direction of arrows A is sufficiently low that gases in the cylinder 12 are able to pass back into the inlet conduit 22 in the direction of arrow B. This causes a significant reduction in the amount of oxygen available for combustion in the cylinder 12 and a reduction in power produced by the cylinder 12. It also prevents the engine from idling smoothly. At elevated rpm, the pressure of air traveling the direction of arrows A is sufficiently high that gases in the cylinder 12 are not able to pass back into the inlet conduit 22 even though both the inlet valve 18 and the outlet valve 20 are open.
In the claims of this application and in the description of the invention, except where the context requires otherwise due to express language or necessary implication, the words “comprise” or variations such as “comprises” or “comprising” are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.